Surge limiting circuit



May 28, 1935. w w, STURDY 2,002,617

sURGE LIMITING CIRCUIT Filed March 2, 1933 hcom Hw@ INVENTOR WWSILwdy BY /p/f. Z QC ATTORNEY Patented May 28, 119,35*;

UNITED STATES PATENT OFFICE SURGE LIMITING CIRCUIT Application March 2,

Claims.

This invention relates to electrical circuits. More particularly, this invention relates to circuits for the transmission of current, and. more particularly for limiting the rate of change of 5 current through said circuits when a so-called short-circuit occurs therein.

in electrical circuits for the transmission of current, a short circuit will occasion a rapid increase in the flew of current through the circuit,

l0 as is well known. Ii a telephone or other circuit is exposed to the circuit which has become snorted, there may be a very large or abnormal voii'age suddenly induced in the telephone or other exposed circuit which may shock or injurethose Aworking with that exposed circuit and, moreover, the induced voltage may be sufficiently great so as to detrimentally aiiect or ruin the apparatus connected or coupled to the exposed circuit.

In accordance with this invention, it is proposed to connect into the current carrying circuit an element which will tend to resist any abnormal increase in the rate of change of current through that circuit, such as may arise from the shorting of that circuit. It is one of the 0bjects of this invention to limit to a controllable extent the maximum voltage which may be induced in a telephone or other circuit which may be exposed to the shorted current carrying circuit.

Another of the objects of this invention is to include in series between a source of electric energy and an energy consuming load a. surgelirniting reactance having such properties that when the current flowing therethrough suddenly tends to rise to an abnormal extent, the voltage set up across the reactance will tend to limit the rate of change of current through the load and thereby reduce below a predetermined value the magnitude of the voltage which may be induced in a telephone or other exposed circuit.

This invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing in which Figure l shows one embodiment of the invention given merely for the purpose of illustration and Fig. 2 shows a curve characteristic cf the reactance which is included in the arrangement shown in Fig. l.

50 Referring to Fig. l of the drawing, the reference character G designates a source of energy and this source may be any well known type of generator either of alternating current or of direct current. The source of energy G is connected to a load M in a series circuit and it will be understood that the load M may be a stationary load or a movable one, the load M at all times receiving current supplied by the source of energy G. In series with the source G and the load M is a reactance designated R which 1933, Serial No. 659,413

includes a coil of wire Wound upon a core of iron or perminvar or other magnetic material, the .reactor R having certain properties which will be described hereinafter in greater detail.

The circuit interconnecting the source of energy G and the load M may be so located with respect to another circuit or telephone line, such as is designated K in the drawing, that voltages may be set up in the line K under normal conditions. These induced voltages may, however, be sufliciently low so that the line K and, moreover, the apparatus connected to the line K may not be adversely aieoted. If the voltages induced in the line K should suddenly rise to an abnormal value as, for example, a voltage of several hundred or several thousand volts, that voltage may be suflicient to seriously injure those who are Working on the line K and also to put out of operation or destroy the apparatus connected or coupled to the line K. In accordance with this invention, the possibility for any of these occurrences will be greatly reduced, as will be apparent from the description hereinafter following.

The reactor R interposed in series between the source of energy G and the load M is one having certain special properties. Its operating characteristic is set forth in Fig. 2 where the magnetomotive force, i. e., the product of a current ilowing through the winding of the reactor R and the number of its turns, is plotted as abscissze against the flux within the core as ordinates. It will be seen that as the magnetomotive force increases up to a certain value, i. e. the value corresponding to the largest abscissa for the curve shown, the core flux increases at a rate which exceeds that of the magnetomotive force. This characteristic curve is different from the typical magnetization curve of ordinary inductive reactors in that the curve bends upward as shown, while the characteristic curve for ordinary reactors is either a straight line or a curve bent down- Ward when plotted against the same abscissae and ordinates.

The inductive reactor R is one whose inductance is a direct function of some elevated power of the current flowing therethrough and it may be represented as follows:

L=KII Here L equals the inductance of the reactor, K its design constant, I the current iiowing through its winding and c: a positive number which is greater than unity. Thus, the use of a reactor which produces an inductance determined by some power of the transmitted current which is greater than unity represents the type of reactor which is characteristic of this invention and this sort of reactor is interposed serially between the source of energy G and the load M. This reactor produces a voltage drop which is Uil quite small under normal conditions. Under abnormal conditions, however, as in the case of a short circuit, the inductance of the reactor R will increase more rapidly than the current in its winding and this will tend to prevent the rate oi' change of current from reaching the abnormal magnitudes which would be obtained if such a reactor were not present in the circuit.

The reactor R may be used in series in any circuit Where it is desired to limit r reduce the voltage effects which might be produced by a short-circuit. It is especially suitable for limiting the rate of change of current in an electried railroad when a short-circuit occurs at the electrical apparatus of any or the trains or at any Y other point on the current containing the reactor and connected or otherwise coupled to the source of energy. Inasrnuch as the circuits for electrified railroad frequently run parallel to telephone lines and other lines carrying signals, it becomes especially important to insert in series with the source of energy of the electried railroadI line a reactor of the type characteristic ofthis invention.

In one form of. the arrangement described herein, using a ferrous alloy suitable for the coreof the reactor of this invention, such an alloy having, for example, a magnetization curve eX- pressed (over the range to be used) by the formula,

Where B: ux density in gausses,

H :magnetizing force in gilberts per centimeter, a reactor might be constructed to have an inductance which when computed according to the equation of line i9 of page l would be .0i27 henry at 3000 amperes and .00141 henry at 1000 amperes. Such` a reactor would have a magnetic coreI of cross-sectional area of 36 square feet and a'total mean core length of 69 feet. The winding would consist of 8.4 turns of Yinsulated conductor of such cross section as to carryy 3000v amperes without overheating.

While this invention has been shown and described incertain particular arrangements. merely for the purpose of illustration, it Will be understood that the general principles of this invention may be. applied to other-and widely varied organizations without departing from the spirit of the invention and the scope oi the appended claims.Y v

What is claimed is:

1. A stationary surge-limiting reactor comprising a coil of wire mounted upon a core of magnetic material of fixed and predetermined dimensions, the magnetic properties of the core being such that the inductance produced by the flow 0f current through the coil is proportional to the nth power of the current as determined by the expression LZKI, where L equals the inductanc'e, K. a constant, I the current and n a positive number greater than unity.

2. A stationary surge-limiting reactor comprising a coil of wire mounted upon av magnetic core of fixed and predetermined dimensions, the magetic properties of the core being such that the magnetomotive force produced by increasing current in the coil will increase at a lesser rate than the magnetic flux in the core.

3. The combination Vci a source of current, a load,v and a surge-iimiting reactor connected in series between the source of current and the load, the magnetic properties of the core oi the surgelimiting reactor being such that the inductance of the surge-limiting reactor will be determined bythe current in its winding in accordance with the expression L=Ii', where L equals the inductance, K a constant, I the current andl n a positive number greater than unity.

The combination of a source of current, a load supplied with current from said. source, a circuit transmitting signals andY exposed to the circuit supplying current from said source to said load, and means for preventing voltages induced from the circuit of thesource ci current into the circuit. transmitting signalsy from exceeding a predetermined value, said means consistingl ot a reactor connected. in series between sm- Vsource or current load, the magnetic properties of, the core c'ithe reactor being such that increasing current the reactor will produce a magnetomotive force which-increases at a lesser rate the flux producedjin its ccre.- f

The combination of a power circuit trans mitting,Y large currents, va circuit transmitting signals which is eXposed'tothe-power circuit, and means for preventing excessive voltages from being induced from the' power circuit into. the circuit transmitting signals at such times as the power circuit becomes shorted, said means comprising a reactor having a winding Wound about a magnetic core, the magnetic properties of: the core of the reactor being such that the flux produced in the core by increasing currents will'Y increase at a greater rate thanthe magnetomotive force.

y WILLIAM, W. STUR'DY. 

